Surgical intervention and grafting are sometimes necessary to restore mechanical function and reconstruct the morphology of bone and cartilage, resulting from trauma, tumors, or abnormal bone developments.
Synthetic materials such as metals, calcium salts and bone cements have also been used for restoring and reconstructing bone for many years, but often result in stress-shielding to the surrounding bone and fatigue failure of the implant. Another possibility is autologous bone grafting, although the supply of autologous bone tissue is limited and bone harvesting is painful, with the risk of infection, hemorrhage, aesthetic damage, nerve damage, and loss of bone function. In addition, significant morbidity is associated with autograft harvest sites. These problems may be overcome by tissue engineering of scaffolds made of synthetic or natural biomaterials that promote the adhesion, migration, proliferation, and differentiation of bone marrow stem cells, also known as mesenchymal stem cells (MSCs). An association between biocomponents and biologic regenerative and repair responses can be promoted by providing a scaffold containing spaces morphologically compatible with osteons and their vascular interconnections.
The immediate microenvironment and the three-dimensional (3D) organization are important factors in differentiation in general and particularly in osteogenic differentiation.
Some bone tissue engineering scaffolds consists of natural polymers, such as collagen, alginate, hyaluronic acid, and chitosan. Natural materials offer the advantages of specific cell interaction, easy seeding of cells because of their hydrophilic interactions, low toxicity and low chronic inflammatory response. However, these scaffolds often are mechanically unstable and do not readily contribute to the creation of tissue structures with a specific predefined shape for transplantation. To obtain mechanical strength, chemical modification is required, which may lead to toxicity.
Defects and degeneration of the articular cartilage surfaces of joints causes pain and stiffness. Damage to cartilage which protects joints can result from either physical injury as a result of trauma, sports or repetitive stresses (e.g., osteochondral fracture, secondary damage due to cruciate ligament injury) or from disease (e.g. osteoarthritis, rheumatoid arthritis, aseptic necrosis, osteochondritis dissecans).
Osteoarthritis (OA) results from general wear and tear of joints, most notably hip and knee joints. Osteoarthritis is common in the elderly but, in fact, by age 40 most individuals have some osteoarthritic changes in their weight bearing joints. Another emerging trend increasing the prevalence of osteoarthritis is the rise in obesity. The CDC estimates that 30% of American adults (or 60 million people) are obese. Obese adults are 4 times more likely to develop knee OA than normal weight adults Rheumatoid arthritis is an inflammatory condition which results in the destruction of cartilage. It is thought to be, at least in part, an autoimmune disease with sufferers having a genetic predisposition to the disease.
Orthopedic prevention and repair of damaged joints is a significant burden on the medical profession both in terms of expense and time spent treating patients. In part, this is because cartilage does not posses the capacity for self-repair. Attempts to re-grow hyaline cartilage for repair of cartilage defects remain unsuccessful.
Orthopedic surgery is available in order to repair defects and prevent articular damage in an effort to forestall serious degenerative changes in a joint. The use of surgical techniques often requires the removal and donation of healthy tissue to replace the damaged or diseased tissue. Techniques utilizing donated tissue from autografts, allografts, or xenografts are wholly unsatisfactory as autografts add additional trauma to a subject and allografts and xenografts are limited by immunological reactivity to the host subject and possible transfer of infective agents. Surgical attempts to utilize materials other than human or animal tissue for cartilage regeneration have been unsuccessful.
The restoration of one or more teeth in a patient's mouth using artificial components is used in implant dentistry. Such artificial components typically include a dental implant and a prosthetic tooth and/or an abutment that is secured to the dental implant.
The dental implant is typically fabricated from pure titanium or a titanium alloy. The dental implant typically includes a body portion and a collar. The body portion is configured to extend into and osseointegrate with the alveolar bone. The top surface of the collar typically lies flush with the crest of the jawbone bone. The abutment (e.g., a final abutment) typically lies on the top surface and extends through the soft tissue, which lies above the alveolar bone. Recently, some dental implants have collars that extend above the crest of the jawbone and through the soft tissue.
Implants of various tapers and with various thread profiles, and comprised of different materials are known in the art.
While such prior art dental implants have been successful, there is a continuing desire to improve a dental implant's ability to osseointegrate with the alveolar bone and to improve the stability of the dental implant within the alveolar bone.
Every year several hundred thousand people require artificial hip, knee or shoulder implants (prostheses). Although such total joint prostheses have been in clinical use for decades, they are still plagued with problems of permanent, rigid fixation. Virtually all implants currently in use have a tendency to loosen with time, some to the extent of requiring revision.
There are two main techniques commonly used for fixation: cemented types using bone cement and uncemented or press-fit types. One bone cement in common use is poly(-methyl methacrylate), which is applied in a dough-like state as a grouting agent between the bone and the implant. It flows around the contours of the bone and the implant and into the interstices of cancellous bone. Upon hardening, the cement forms a mechanical interlock between the bone and the implant. In effect, there is no bone in-growth linking bone and prosthesis when bone cement is used. Although bone cement gives good initial fixation, an increase in compliance often occurs due to formation of a soft tissue capsule over time. Thus, the absence of bone in-growth frequently leads to loosening of a bone-cemented prosthesis.
Press-fit prostheses are not implanted with bone cement but rather into a prepared cavity in the bone which closely approximates the prosthetic shape; long term stability of such implants requires bone to form an interlock by growing into the prosthesis at the mating surface.
Certain osteo-conductive materials (e.g., hydroxyl-apatite applied by plasma-spraying) are favored for their durability and bonding strength, but obtaining the desired press-fit at surgery is often associated with problems (Geesink, R. G. T., Clinical Orthopedics and Related Research, 261:39-58 (1990)). Further, the cavity prepared in bone to receive the prosthesis is generally not optimally shaped, causing the actual bone contact achieved with insertion of the prosthesis to be only 10-20% of the potential mating surface. The remaining voids between bone and prosthesis, containing little or no osteo-conductive material, contribute little to the bone-prosthesis interlock necessary for long-term stability of the prosthesis. There remains a need for improved prosthetic devices providing enhanced bone-prosthesis attachment stability.
Pain due to severe osteoarthritis may be associated with “intraosseous hypertension,” i.e., pressure within the bone. Intra-osseous hypertension is the manifestation of edema within the bone. Thus, it has been proposed that local vascular changes may be important in the pathogenesis of degenerative arthritis and the production of its associated symptoms. It has been further observed that surgical decompression of bone (specifically in the case of osteonecrosis) can relieve bone pain. Use of surgery, however, to alleviate pressure within the bone is not ideal. For one thing, surgery can produce myriad side effects and complications, but more to the point, the problem with surgical decompression is that its benefit will be transient. The fenestrations created during so-called decompressive procedures are bound to fill with fibrocartilage. Thus, there is an ongoing need for a safe and effective method for alleviating pressure in bone causing joint pain, most typically found in patients suffering from osteoarthritis.
An ideal material which restores mechanical function and reconstructs the morphology of bone and cartilage, and/or serves as an appropriate implant material for tissue reconstructive purposes, is as yet, lacking.